This invention relates to a tire; more particularly to a pneumatic tire capable of being used in the uninflated condition.
Various tire constructions have been suggested for pneumatic runflat tires, that is, tires capable of being used in the uninflated condition. One approach described in U.S. Pat. No. 4,111,249 entitled xe2x80x9cBanded Tiresxe2x80x9d was to provide a hoop or annular band directed under and approximately as wide as the tread. The hoop in combination with the rest of the tire structure could support the vehicle weight in the uninflated condition. This banded tire actually tensioned the ply cords even in the uninflated condition. Another U.S. Pat. No. 5,685,927; combined the use of sidewall inserts in combination with an annular bead placed directly under the tread. In this approach, the sidewall inserts were assisted in load carrying capacity by the addition of this tread bead. The resultant tire was able to carry more load with less sidewall material. Unfortunately, the hoop or beads under the tread created additional rolling resistance problems and presented a much stiffer tread area which could inhibit ride performance.
In a 1998 article entitled xe2x80x9cSelf-Supporting Tire Performance Criteria in Testingxe2x80x9d, the author Walter Lee Willard, Jr. of Michelin America Research and Development corporation, reported to the Society of Automotive Engineers, Inc. a rather comprehensive study of self-supporting tires. He reported that self-supporting tires share the same basic design objectives: minimize the differences relative to conventional tires (inflated), enhance low pressure handling capability, acceptable zero PSI handling on suitable vehicles, enhance low pressure and zero PSI bead retention; and provide sufficient zero PSI durability to avoid a less than ideal roadside situation.
It is applicants"" belief that the ideal self-supporting or runflat tires is one that can operate at zero PSI indefinitely and this theoretical tire should provide the same ride performance and handling characteristics of the pneumatic tire. Having set that, as a design goal, current technology falls far short in several areas, however, it is improving rapidly. In order to approach the theoretical goal, applicants have discovered several unique relationship with regard to runflat tires, and in discovering these relationships, they have developed several embodiments that have improved characteristics and are a great step forward in the achievement of the theoretical runflat tire.
A pneumatic runflat tire 1, 2, 3, 4, 5 or 6 having a radially outer tread 12, a belt reinforcing structure radially inward of the tread, the belt reinforcing structure having at least two cord reinforced layers 24, 26, and a carcass reinforcing structure including at least one cord reinforced ply 30, 32 extending to a pair of annular beads 36a, 36b is disclosed. The tire when mounted on a design rim when normally inflated but unloaded has a section height (H), a section width W, wherein W is greater than (H). The tire has a pair of sidewalls 16, 18 extending from the tread 12 radially inward toward the bead cores 36a, 36b. Each sidewall 16, 18 has at least one elastomeric filler 40a, 40b, 42a, 42b radially inward of the ply 30, 32. The normally inflated 30 PSI deflection D30 of the tire when under normal vehicle load is less than 20 mms. The zero PSI deflection D0 under normal load is less than 40 mms. The difference between the vehicle loaded uninflated deflection D0 minus the D30 deflection is substantially equal to or less than the amount of deflection D30. 
The tire 1, 2, 3, 4, 5 and 6 when mounted on a design rim and normally inflated and placed under normal vehicle load, has a dynamic tread contact patch 55 at 4 kph or greater characterized by a substantially rectangular shape having a width Wn and a average circumferential length Ln and a length Ln+xcex94L and width W0; wherein W0 is less the 120% of Wn when under normal vehicle load and zero inflation pressure. The contact patch 55 has a parimeter shape wherein at least the leading edge 54 and preferably some or all the trailing edge 56 maintains tread element contact in the range of inflation pressures from zero to normal inflation pressure. The ratio of the contact patch length Ln+xcex94L at zero PSI to the length Ln is 225 percent or less. The tire 1, 2, 3, 4, 5 and 6 has a net contact area when normally vehicle loaded and inflated that is less than 150 percent of the normally vehicle loaded and zero PSI net contact area, preferably less than 125%, most preferably the same contact area.
The pneumatic runflat tires achieving this deflection at 30 PSI and zero PSI and the footprint contact shape are defined by a combination of composite structures which include the tread 12, the belt reinforcing structure 24, 26 and the at least one cord reinforced ply 30, 32 and one or more tread stiffening members 101 selected from a group of one or more of the following: a) a fabric overlay 28 having at least three layers of cord reinforced material located between the tread 12 and the belt reinforcing structure 24, 26, b) at least three or more annular bands 29 positioned in an array laterally across the tire 4 interposed between the belt reinforcing structure 24, 26 and the carcass ply 30, 32, the array of bands 29 having axial width at least 70 percent of the tread width, c) one or more layers of elastomeric spacers 27 xe2x80x94one layer located between two belt layers 24, 25, 26 or a belt layer 26 and a carcass ply 30, 32, d) a third belt layer 25 having steel cords inclined in a range of 18xc2x0 to 30xc2x0 relative to the tires equatorial plane, e) a third belt layer 25 having cords in a range of 50xc2x0 to 80xc2x0 relative to the equatorial plane and located between the belt structure and the carcass ply, f) one or more fabric underply layers 70 located between the belt reinforcing structure 24, 26 and the carcass reinforcing structure 30, 32, g) one or more helically wound coils 60 extending circumferentially around and radially inward of the belt reinforcing structure 24, 26, the combination of elements forming a composite structure yielding the contact patch 55 at normal inflation and zero PSI whereby the tread elements maintain at least parimeter contact around the contact patch 55, at both shoulder regions 50, 52 and the leading edge 54, preferably at both shoulder regions 50, 52, and leading edge 55 and trailing edge 56.
The tire 1, 2, 3, 4, 5 or 6 when employing one or more of the stiffening members 101 described above achieves the desired zero PSI driving and handling performance without sacrificing the tire""s ride and handling at normal inflation pressures.
A preferred embodiment tire 1 includes a fabric overlay 28 interposed between the tread 12 and the belt reinforcing structure 24, 26, the fabric overlay 28 being made of three or more spirally wound layers of aramid reinforced strips. The cords of the fabric overlay 28 are oriented at an angle xcex8 of less than 5xc2x0 relative to an equatorial plane of the tire 1. The fabric overlay 28 is preferably composed of strips which are spirally wound about the tire, its spiral revolution having a pitch of about 25 mm or less. In tires 1 having an aspect ratio greater than 50% the strips overlap sufficiently to create at least three layers of overlay fabric 28 across the entire width of the overlay 28. In tires 1 having an aspect ratio of less than 50% the strips are overlapped in three layers in at least the central region and the shoulder regions, the three layers covering at least 60% of the overlay width.
Another embodiment tire 2 according to the invention has a belt reinforcing structure having three belt layers 24, 25, 26, each belt layer 24, 25, 26 having parallel cords oriented angularly relative to the equatorial plane of the tire 2 in the range of 18xc2x0 to 30xc2x0; each adjacent layer being oppositely inclined relative to another layer. In the preferred second embodiment tire 2, each belt layer is similarly but oppositely inclined. The cords of one or more belt layers are steel and have a diameter of 0.035 inches and a 2+2 construction. Alternatively, the cords of one or more belt layers can be made of steel having a diameter of 0.056 inches. The second embodiment tire 2 described above further may include a fabric overlay 28, the overlay 28 having two layers of preferably aramid reinforced cords, preferably the cords are applied and spirally wound strips. Alternatively, the three-belt layer tire may have one belt larger 24, 25, or 26 having cords oriented at 50xc2x0 to 90xc2x0 relative to the equatorial plane. The tread stiffening member 101 in the third through fifth embodiment, tires 3, 4, 5, 6 include three or more resilient bands 29, a helically wound coil 60 and elastomeric spacer layers 27, and a fabric underply respectively.
Definitions
xe2x80x9cAspect Ratioxe2x80x9d means the ratio of its section height to its section width.
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d means the lines or directions that are parallel to the axis of rotation of the tire.
xe2x80x9cBeadxe2x80x9d or xe2x80x9cBead Corexe2x80x9d means generally that part of the tire comprising an annular tensile member, the radially inner beads are associated with holding the tire to the rim being wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes or fillers, toe guards and chafers, the bead or beads under the tread being encapsulated in tread rubber can be with or without other cord reinforced fabric elements.
xe2x80x9cBelt Structurexe2x80x9d or xe2x80x9cReinforcing Beltsxe2x80x9d means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17xc2x0 to 27xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.
xe2x80x9cCarcassxe2x80x9d means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
xe2x80x9cCasingxe2x80x9d means the carcass, belt structure, beads, sidewalls and all other components of the tire excepting the tread and undertread.
xe2x80x9cChafersxe2x80x9d refers to narrow strips of material placed around the outside of the bead to protect cord plies from the rim, distribute flexing above the rim.
xe2x80x9cCordxe2x80x9d means one of the reinforcement strands of which the plies in the tire are comprised.
xe2x80x9cEquatorial Plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread.
xe2x80x9cFootprintxe2x80x9d means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load and pressure.
xe2x80x9cInnerlinerxe2x80x9d means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid within the tire.
xe2x80x9cNormal Inflation Pressurexe2x80x9d means the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cNormal Loadxe2x80x9d means the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cNormal Vehicle Loadxe2x80x9d means the estimated load for a given tire at a predetermined vehicle specified pressure. For this application, all testing was conducted at 900 lbs. load at 30 psi, 0 psi unless otherwise indicated for a 215/65R15 sized tire.
xe2x80x9cPlyxe2x80x9d means a continuous layer of rubber-coated parallel cords.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d mean directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cRadial Ply Tirexe2x80x9d means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65xc2x0 and 90xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cSection Heightxe2x80x9d means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.
xe2x80x9cSection Widthxe2x80x9d means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands.
xe2x80x9cShoulderxe2x80x9d means the upper portion of sidewall just below the tread edge.
xe2x80x9cSidewallxe2x80x9d means that portion of a tire between the tread and the bead.
xe2x80x9cTread Widthxe2x80x9d means the arc length of the tread surface in the axial direction, that is, in a plane parallel to the axis of rotation of the tire.